Known curtainwall systems including known skylight systems typically include a series of generally parallel rafters attached to a series of purlins which are usually interconnected perpendicular to the rafters. The rafters and purlins provide a framework to support glass panes or panes made of other materials. Such a rafter and purlin structural framework is typically attached to the superstructure of a building.
U.S. Pat. No. 4,621,472 issued to Kloke shows such a framing system, wherein the glazing sheets are directly supported by both rafters and purlins. One of the major problems with skylight systems is providing a structure which will repel water. The glass panes are usually secured to the rafter and purlin framework in part by pressure plates which, when supplemented by gaskets or the like, provide a seal between the glass sheets and the plate. However, water can penetrate the seal. Kloke teaches the use of drainage channels in both rafters and purlins. Water which passes by the seals will enter drainage channels in the purlins and then be discharged into the drainage channels in the rafters and thereafter be removed from the structural system. Kloke also teaches the use of channels along the length of the purlins to trap condensation that collects on the inside of the glass panes and also provides for discharge into the drainage channels of the rafters. The system disclosed by Kloke shows an interconnection between the purlin and the rafter wherein an overlapping portion of the purlin is supported in a cut-out portion through the side of the rafter.
Other such structural systems which include similar drainage means are disclosed in U.S. Pat. No. 4,680,905 which issued to Rockar and U.S. Pat. No. 4,850,167 which issued to Beard et al.
However all these known systems utilize the same basic principle of providing a framework system to which the panes are secured in the field. In such systems the structural framework of rafters and purlins is first constructed in the field and then the panes are installed. Although a seal between purlins and panes is created by a pressure plate, this seal is sometimes not very effective and can leak. Also, the drainage channels in the purlins can overflow. Another drawback is that the seal at the interconnection between the purlins and rafters can sometimes fail or be ineffective. In a system where there is a cut-out in the supporting rafter to support the purlin, there is a particular vulnerability at the cut-out for a leak or overflow. Further, assembly in the field is time consuming.
The structural system of this invention seeks to overcome the drawbacks of the known systems.